1. Field of the Invention
This invention relates to a bonding method to perform wire bonding to an electrode pad formed on a semiconductor chip, etc.
2. Background Art
Known wire bonding methods utilize ultrasonic vibrations to electrically connect electrode pads of semiconductor chips to leadframes, wiring substrates, other semiconductor chips, and the like (for example, JP-A 2004-241712 (Kokai)).
Although gold is often used for conventional bonding wire, the sudden rise in the price of gold particularly in recent years has increased the need to use wires of inexpensive copper or copper alloy. However, copper is considerably harder than gold. Therefore, when bonding a wire end portion to the electrode pad, it is necessary to increase the impact load of a ball of the wire end portion on the electrode pad to deform the ball enough to ensure the desired bonding strength. Thereby, concerns remain that wire bonding using copper unfortunately causes damage such as cracks of the electrode pad, semiconductor chip, etc., and discrepancies in which a portion of the electrode pad below the ball is pressed out from around the ball. Due to such problems, gold wires currently are used overwhelmingly as bonding wires even though copper is less expensive than gold.